davey



(No Model.) 2 Sheets-Sheet 2.

H. DAVEY. Differential Valve Gear of Steam Engines. No. 239,228. 7 Patented March 22,1881;

N. PETERSv PHDTO-L|TMOGRAPKER. WASHINGTON. D C

UNITED STATES PATENT Genres.

HENRY DAVEY, F CLARENDON ROAD, LEEDS, COUNTY OF YORK, ENGLAND.

DIFFERENTIAL VALVE-GEAR OF STEAM-ENGINES.

SPECIFICATION forming part. of Letters Patent N0. 239,228, dated March 22, 1881.

Application filed January 20, 1881. (No model.) Patented in England July 26, 1880.

which forms the subject of former patents granted to me is now largely used; but in order that my present invention may be more clearly understood, I will, in the first place, de scribe generally the usual form of differential gear employed for working the slide-valve of a steam-engine.

A lever termed the differential lever is at one end linked to the en gine-pistom'or to some part of the engine moving in time with the piston. At its other end the differential lever is linked to a piston working in an auxiliary cylinder and controlled in its motion by the resistance of liquid to a piston in a cataract. cylinder. At or about its middle the differential lever is linked to the main. slide, which thus receives a differential motion, partly from the auxiliary piston, which moves it so as to open the steam-port, and partly from the main piston, which moves it so as to close the steamport. Thus, supposing the main piston to be at one end of its stroke, and to be stationary, or nearly so, then the auxiliary piston moves the slide so as to admit steam to act on the main piston, and the main piston,in making its stroke, moves back the slide, so as to out 0d the supply of steam, and it does this the sooner the more rapidly it moves, because in that case it outruns the auxiliary piston, which advances at a rate governed by the cataract, tendingto open or to keep open the supply-port.

Now, the object of my present invention is to provide means for arresting the movement of the auxiliary piston at any desired point of its stroke, so that the slide moved by it, while it has a definite lead in advance of the motion of the main piston, may remain practically stationary during part of that motion, instead of being rapidly opened and then gradually closed. I also provide means for compensating inequality of resistance to the motion of the main piston in its forward and backward strokes without having recourse to the heavy counter-weights which are often employed for this purpose, particularly in pumping-engines. I will describe the construction and arrangement which I adopt for this purwhich'is linked to an arm on a rocking shaft,

X. This rocking shaft has on it a long lever, Y, which is linked to an arm, D, projecting down rigid from G, the cross-head of the main piston. The differential lever E is, at about its middle, linked to G, the rod of the main slide M. On the slide-rod G are fixed two adjustable stops, K and L, one on each side ofa stationaryabutment, which consists of a bracket, H, firmly secured in a fixed position, and through which the slide-rod works. It is by means of these stops K and L that the movement of the slide is determined, as I will now explain.

If the differential gear were made in the usual way without stops, such as K and L, then whenthe main piston reached the end of its stroke, the point F remaining practically stationary for a time, the point Z could be moved its full stroke by the piston of the auxiliary cylinder B, and the point G, with the main slide linked to it, would consequently make its complete stroke, opening fully the steam-port, which would .thereafter be gradually closed by the movement of the point F in time with the main piston. Thus the steam-port might be fully opened before the commencement of the stroke of the main piston, and as the piston made its stroke there would he a gradual cutoff. By introducing the stops K and L a different result is obtained, as follows: The auxiliary piston of B is prevented from making its full stroke at once by one or other of the stops K or L coming in contact with the abutment or bracket H, the slide M nevertheless making its full stroke. The pointF then beginning to move in one direction, the lever E for a time merely turns on the rod G as a fulcrum, the point Z continuing to move with the auxiliary piston in the direction opposite to F until Z, having completed its stroke and come to rest, the continued motion of F is imparted to the rod Gr, closing the steam-port. Thus when the main piston is at either extreme of its stroke the sequence of operation is as follows: The main piston begins to move, and the auxiliary piston still continuing to move in time with it, the main slide remains stationary, keeping the steam-port for a time open. When the auxiliary piston has completed its stroke the main piston, continuing its stroke, moves back the slide, closing the steam-port.

In order to compensate inequality in the two strokes of the main piston I, apply a sliding plate, N, on the back of the main slide M. This plate can be moved to or fro by turning a screwed rod, 0, by an external hand-wheel, P, so as to be made to cover, more or less, either of the steam-passages through the slide M, and so to throttle the steam-supply while the piston is makingitslighter stroke, permitting the full supply to be given for the heavier stroke. This arrangement is particularly advantageous when it is applied to the slide of the larger or low-pressure cylinder of a compound engine, because the throttling of the supplyto the one end of the cylinder not only reduces the power of the one stroke when less power is required, but also insures the retention of an increased supply of steam for effectin g the other stroke of the low-pressure piston when greater power is required to overcome the greater load.

Having thusdescribed the nature of my invention, and the best means I know of carrying it out in practice, I would have it understood that I. make no general claim to differential valve-gear for steam-engines, as such gear has already formed the subject of patents andis largely used; but

i claim 1. In differential valve-gear for steam-engines, the combination, with a slidevalve moved differentially, substantially as described, of a stationary abutment and adjustablc stops arranged upon the valve-rod on opposite sides of said abutment, substantially as and for the purposes described.

2. In differential valve-gear for steam-engines, the combination, with the cylinder, piston, slide-valve and its rod and connecting devices, arranged to differentially move the slide-valve, of the stops adjustably secured to the valve-rod and arranged on opposite sides of a stationary abutment, all substantially as and for the purposes described.

In testimony whereof I have hereunto signed my name to this specification, in the presence of two subscribing witnesses, this 20th day of December, A. D. 1880.

H ENRY DAVEY.

Witnesses:

A. V. DOCKERY, GHAs. GILLIARD. 

